- This level occupies the map slot MAP07. For other maps which occupy this slot, see Category:MAP07.
Map07: The Underwater Lab is a level for Harmony.
- Get the chaingun, and go through the back vent.
- Shoot the southern cracked pipe to raise the water level. Then, shoot the other pipe on the fire extinguisher to blow open the pipe.
- Continue down the corridor, drop down, and turn left. You will be attacked by critters, visible by two cyan dots. Follow the left-hand wall, and you should eventually see a switch. Approaching it lights up a few rooms, and pressing up raises the laser barrier to the south west. (The south-east laser barrier will never open.)
- Head through the barrier, and through several rooms. At the end, climb up the stairs, turn left. You should be able to reach the lab area again.
- Go to the north-west of the area, and go into the monster pits. You should eventually reach a switch that allows access to the two locked doors. Look for the green key, in the north-east room of this center area.
- Continue west. There is an optional message that you can read if you want, as it described what happened in the game (although you would know most of it if you read the backstory). To continue, go south into the mossy area.
- Take the branch that leads north. Jump into the pit, and flip the switch to allow access to the rest of the map. Head south to climb back up to where you took the branch.
- Take the next south branch, and look for a path to the west. Continue following the path as it turns right leads to the violet key. Continue further for a quicker route to the train.
- Now, head north. When you get to the broken bridge with electrified floor, look for a hole in the north-east corner.
- When you reach the autodestruct, you need to run towards the train within a few seconds. If you don't make it, you will be caught in the detonations.
- At walkthrough step 5, there is a dark corridor on the south-west wall. Entering it leads to a 100% health bonus.